Method for recording data on optical recording medium, device for recording data on optical recording medium, and optical recording medium

ABSTRACT

It is an object of the present invention to provide a method for recording data in an optical recording medium which can record data in a write-once type optical recording medium at a high linear recording velocity using a laser beam whose recording power is set low. The method for recording data in an optical recording medium according to the present invention is constituted so that data are recorded by a laser beam whose power is modulated in accordance with a pulse train pattern onto an optical recording medium including a substrate, a first recording layer, a second recording layer and a light transmission layer to form a recording mark wherein a recording pulse is divided into (n−1) divided pulses and the power of the laser beam is set to a recording power Pw at the peak of each of the divided pulses and set to a first bottom power Pb 1  and the levels of the recording power Pw and the first bottom power Pb 1  are determined so that a ratio Pb 1 /Pw of the first bottom power Pb 1  to the recording power Pw falls within a range of 0.1 to 0.5. When the power of a laser beam is modulated using such a pulse train pattern to record data in an optical recording medium, the heating of a recording layer by the laser beam having the recording power Pw can be augmented by the laser beam having the first bottom power Pb 1  and therefore, even in the case where data are to be recorded in an optical recording medium at a high linear recording velocity, it is possible to record data in the optical recording medium at a high linear recording velocity using a semiconductor laser having a low output.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a method for recording data in anoptical recording medium, an apparatus for recording data in an opticalrecording medium and an optical recording medium, and particularly, to amethod for recording data in a write-once type optical recording medium,an apparatus for recording data in a write-once type optical recordingmedium, and a write-once type optical recording medium.

2. Description of the Related Art

Optical recording media such as the CD, DVD and the like have beenwidely used as recording media for recording digital data. These opticalrecording media can be roughly classified into optical recording mediasuch as the CD-ROM and the DVD-ROM that do not enable writing andrewriting of data (ROM type optical recording media), optical recordingmedia such as the CD-R and DVD-R that enable writing but not rewritingof data (write-once type optical recording media), and optical recordingmedia such as the CD-RW and DVD-RW that enable rewriting of data (datarewritable type optical recording media).

As well known in the art, data are generally recorded in a ROM typeoptical recording medium using pre-pits formed in a substrate in themanufacturing process thereof, while in a data rewritable type opticalrecording medium a phase change material is generally used as thematerial of the recording layer and data are recorded utilizing changesin an optical characteristic caused by phase change of the phase changematerial.

On the other hand, in a write-once type optical recording medium, anorganic dye such as a cyanine dye, phthalocyanine dye or azo dye isgenerally used as the material of the recording layer and data arerecorded utilizing changes in an optical characteristic caused bychemical change of the organic dye, or chemical change and physicalchange of the organic dye.

Further, there is known a write-once type recording medium formed bylaminating two recording layers (See Japanese Patent Application LaidOpen No. 62-204442, for example) and in this optical recording medium,data are recorded therein by projecting a laser beam thereon and mixingelements contained in the two recording layers to form a region whoseoptical characteristic differs from those of regions therearound.

In this specification, in the case where an optical recording mediumincludes a recording layer containing an organic dye, a region in whichan organic dye chemically changes or chemically and physically changesupon being irradiated with a laser beam is referred to as “a recordingmark” and in the case where an optical recording medium includes tworecording layers each containing an inorganic element as a primarycomponent, a region in which the inorganic elements contained in the tworecording layers as a primary component are mixed upon being irradiatedwith a laser beam is referred to as “a recording mark”.

An optimum method for modulating the power of a laser beam projectedonto an optical recording medium for recording data therein is generallycalled “a pulse train pattern” or “recording strategy”.

FIG. 9 is a diagram showing a typical pulse train pattern used forrecording data in a CD-R including a recording layer containing anorganic dye and shows a pulse train pattern for recording 3 T to 11 Tsignals in the EFM Modulation Code.

As shown in FIG. 9, in the case where data are to be recorded in a CD-R,a recording pulse having a width corresponding to the length of arecording mark M to be formed is generally employed (See Japanese PatentApplication Laid Open No. 2000-187842, for example).

More specifically, the power of a laser beam is fixed to a bottom powerPb when the laser beam is projected onto a blank region in which norecording mark M is formed and fixed to a recording power Pw when thelaser beam is projected onto a region in which a recording mark M is tobe formed. As a result, an organic dye contained in a recording layer isdecomposed or degraded at a region in which a recording mark M is to beformed and the region is physically deformed, thereby forming arecording mark M therein. Here, the linear recording velocity is about1.2 m/sec at a 1× linear recording velocity of a CD-R.

FIG. 10 is a diagram showing a typical pulse train pattern used forrecording data in a DVD-R including a recording layer containing anorganic dye and shows a pulse train pattern for recording a 7 T signalin the 8/16 Modulation Code.

Since data are recorded in a DVD-R at a higher linear recording velocitythan when recording data in a CD-R, unlike the case of recording data ina CD-R, it is difficult to form a recording mark having a good shapeusing a recording pulse having a width corresponding to the length ofthe recording mark M to be formed.

Therefore, data are recorded in a DVD-R using a pulse train in which, asshown in FIG. 11, the recording pulse is divided into a number ofdivided pulses corresponding to the length of the recording mark M to beformed.

More specifically, in the case of recording an nT signal where n is aninteger equal to or larger than 3 and equal to or smaller than 11 or 14in the 8/16 Modulation Code, (n−2) divided pulses are employed and thepower of the laser beam is set to a recording power Pw at the peak ofeach of the divided pulses and set to a bottom power Pb at the otherportions of the pulse. In this specification, the thus constituted pulsetrain pattern is referred to as “a basic pulse train pattern”. Here, thelinear recording velocity is about 3.5 m/sec at a 1× linear recordingvelocity of a DVD-R.

As shown in FIG. 10, in the basic pulse train pattern, the level of abottom power Pb is set equal to a reproducing power Pr used forreproducing data or close thereto.

On the other hand, a next-generation type optical recording medium thatoffers improved recording density and has an extremely high datatransfer rate has been recently proposed.

In such a next-generation type optical recording medium, in order toachieve an extremely high data transfer rate, it is required to recorddata at a higher linear recording velocity than that in a conventionaloptical recording medium, and since the recording power Pw necessary forforming a recording mark is generally substantially proportional to thesquare root of the linear recording velocity in a write-once opticalrecording medium, it is necessary to employ a semiconductor laser havinga high output for recording data in a next-generation optical recordingmedium.

Further, in the next-generation type optical recording medium, theachievement of increased recording capacity and extremely high datatransfer rate inevitably requires the diameter of the laser beam spotused to record and reproduce data to be reduced to a very small size.

In order to reduce the laser beam spot diameter, the numerical apertureof the objective lens for condensing the laser beam needs to beincreased to 0.7 or more, for example, to about 0.85, and the wavelengthof the laser beam needs to be shortened to 450 nm or less, for example,to about 400 nm.

However, the output of a semiconductor laser emitting a laser beamhaving a wavelength equal to or shorter than 450 nm is smaller than thatof a semiconductor laser emitting a laser beam having a wavelength of780 nm for a CD and that of a semiconductor laser emitting a laser beamhaving a wavelength of 650 nm for a DVD, and a semiconductor laser thatemits a laser beam having a wavelength equal to or shorter than 450 nmand has a high output is expensive.

Therefore, it is difficult to record data in a next-generation typeoptical recording medium using the basic pulse train pattern at a highdata transfer rate and this problem is particularly serious whenrecording data at a linear recording velocity equal to or higher than 5m/sec.

BRIEF SUMMARY OF THE INVENTION

It is therefore an object of the present invention to provide a methodfor recording data in an optical recording medium which can record datain a write-once type optical recording medium at a high linear recordingvelocity.

It is another object of the present invention to provide a method forrecording data in an optical recording medium which can record data in awrite-once type optical recording medium using a laser beam whoserecording power is set low.

It is a further object of the present invention to provide a method forrecording data in an optical recording medium which can record data in awrite-once type optical recording medium at a high linear recordingvelocity using an inexpensive semiconductor laser having a low output.

It is a further object of the present invention to provide a method forrecording data in an optical recording medium which can record data in awrite-once type optical recording medium including two or more recordinglayers at a high linear recording velocity.

It is a further object of the present invention to provide an apparatusfor recording data in an optical recording medium which can record datain a write-once type optical recording medium at a high linear recordingvelocity.

It is a further object of the present invention to provide an apparatusfor recording data in an optical recording medium which can record datain a write-once type optical recording medium using a laser beam whoserecording power is set low.

It is a further object of the present invention to provide an apparatusfor recording data in an optical recording medium which can record datain a write-once type optical recording medium at a high linear recordingvelocity using an inexpensive semiconductor laser having a low output.

It is a further object of the present invention to provide an apparatusfor recording data in an optical recording medium which can record datain a write-once type optical recording medium including two or morerecording layers at a high linear recording velocity.

It is a further object of the present invention to provide an opticalrecording medium in which data can be recorded at a high linearrecording velocity.

It is a further object of the present invention to provide an opticalrecording medium in which data can be recorded using a laser beam whoserecording power is set low.

It is a further object of the present invention to provide an opticalrecording medium in which data can be recorded at a high linearrecording velocity using an inexpensive semiconductor laser having a lowoutput.

It is a further object of the present invention to provide an opticalrecording medium including two or more recording layers in which datacan be recorded at a high linear recording velocity.

The inventors of the present invention vigorously pursued a study foraccomplishing the above objects and, as a result, made the discoverythat when the ratio Pb1/Pw of a first bottom power Pb1 to a recordingpower Pw was set to 0.1 to 0.5, the heating of a recording layer by thelaser beam having the recording power Pw was augmented by the laser beamhaving the first bottom power Pb1 and it was possible to record data inan optical recording medium with a lower recording power even in thecase where data were to be recorded at a high linear recording velocity.

Therefore, the above objects of the present invention can beaccomplished by a method for recording data in an optical recordingmedium wherein data are recorded in a write-once type optical recordingmedium comprising a substrate and at least one recording layer formed onthe substrate by projecting a laser beam whose power is modulated by apulse train pattern including at least a pulse whose level is set to alevel corresponding to a recording power and a pulse whose level is setto a level corresponding to a first bottom power onto the at least onerecording layer and forming at least two recording marks in the at leastone recording layer, the method for recording data in an opticalrecording medium comprising a step of setting a ratio Pb1/Pw of a firstbottom power Pb1 to a recording power Pw to 0.1 to 0.5.

In this specification, in the case where an optical recording mediumincludes a recording layer containing an organic dye, a region in whichthe organic dye chemically changes or chemically and physically changesupon being irradiated with a laser beam is referred to as a “recordingmark” and in the case where an optical recording medium includes tworecording layers each containing an inorganic element as a primarycomponent, a region in which the inorganic elements contained in the tworecording layers as a primary component are mixed upon being irradiatedwith a laser beam is referred to as a “recording mark”.

According to the present invention, since the ratio Pb1/Pw of the firstbottom power Pb1 to the recording power Pw is set to 0.1 to 0.5, theheating of a recording layer by the laser beam having the recordingpower Pw can be augmented by the laser beam having the first bottompower Pb1 and it is therefore possible to record data in an opticalrecording medium with a lower recording power even in the case wheredata are to be recorded at a high linear recording velocity.

Further, according to the present invention, since the ratio Pb1/Pw ofthe first bottom power Pb1 to the recording power Pw is set to 0.1 to0.5, the heating of a recording layer by the laser beam having therecording power Pw can be augmented by the laser beam having the firstbottom power Pb1 and it is therefore possible to record data in anoptical recording medium at a high linear recording velocity using aninexpensive semiconductor laser having a low output.

In a preferred aspect of the present invention, data are recorded at alinear recording velocity equal to or higher than 5 m/sec.

In a preferred aspect of the present invention, the optical recordingmedium further comprises a light transmission layer, and a firstrecording layer and a second recording layer formed between thesubstrate and the light transmission layer, and is constituted so thatthe at least two recording marks are formed by projecting the laser beamthereonto, thereby mixing an element contained in the first recordinglayer as a primary component and an element contained in the secondrecording layer as a primary component.

In a further preferred aspect of the present invention, the secondrecording layer is formed so as to be in contact with the firstrecording layer.

In a preferred aspect of the present invention, the at least tworecording marks are formed by setting a ratio of the shortest blankregion interval to a linear recording velocity to equal to or smallerthan 40 nsec.

In a preferred aspect of the present invention, data are recorded at alinear recording velocity equal to or higher than 10 m/sec by settingthe ratio Pb1/Pw of the first bottom power Pb1 to the recording power Pwto 0.2 to 0.5.

In a further preferred aspect of the present invention, the at least tworecording marks are formed by setting a ratio of the shortest blankregion interval to a linear recording velocity equal to or smaller than20 nsec.

In a further preferred aspect of the present invention, the ratio Pb1/Pwof the first bottom power Pb1 to the recording power Pw is set to 0.3 to0.45.

In a preferred aspect of the present invention, the pulse whose level isset to a level corresponding to the recording level is constituted bydivided pulses of a number corresponding to a length of the recordingmark.

In a further preferred aspect of the present invention, the power of thelaser beam is modulated in accordance with a pulse train patternincluding a pulse whose level to set to a level corresponding to asecond bottom power lower than the first bottom power after the pulsewhose level is set to a level corresponding to the recording level.

In a preferred aspect of the present invention, the first bottom powerand the recording power are set so that AH is larger than AL, where ALis a ratio of the first bottom power to the recording power when dataare to be recorded at a first linear recording velocity and AH is aratio of the first bottom power to the recording power when data are tobe recorded at a second linear recording velocity higher than the firstlinear recording velocity.

In a further preferred aspect of the present invention, the first bottompower and the recording power are set so that AH is larger than 1.5*ALand smaller than 5.0*AL.

In a further preferred aspect of the present invention, the first bottompower and the recording power are set so that AH is larger than 2.5*ALand smaller than 4.0*AL.

In a further preferred aspect of the present invention, the first linearrecording velocity is set equal to or higher than 5 m/sec and the secondlinear recording velocity is set equal to or higher than 10 m/sec.

In a preferred aspect of the present invention, data are recorded in theoptical recording medium by projecting a laser beam having a wavelengthequal to or shorter than 450 nm thereonto.

In a preferred aspect of the present invention, data are recorded in theoptical recording medium by employing an objective lens and a laser beamwhose numerical aperture NA and wavelength λ satisfy λ/NA≦640 nm, andprojecting the laser be/m onto the optical recording medium via theobjective lens.

The above objects of the present invention can be also accomplished byan apparatus for recording data in an optical recording medium, whichcomprises a laser beam projecting means for projecting a laser beamwhose power is modulated by a pulse train pattern including at least apulse whose level is set to a level corresponding to a recording powerand a pulse whose level is set to a level corresponding to a firstbottom power onto a write-once type recording medium comprising asubstrate and at least one recording layer formed on the substrate, thelaser beam projecting means being constituted so as to modulate thepower of the laser beam in accordance with the pulse train pattern inwhich a ratio Pb1/Pw of the first bottom power Pb1 to the recordingpower Pw is set to 0.1 to 0.5.

In a preferred aspect of the present invention, data are recorded at alinear recording velocity equal to or higher than 5 m/sec.

In a preferred aspect of the present invention, a ratio of the shortestblank region interval to a linear recording velocity is set equal to orsmaller than 40 nsec.

In a preferred aspect of the present invention, data are recorded at alinear recording velocity equal to or higher than 10 m/sec by settingthe ratio Pb1/Pw of the first bottom power Pb1 to the recording power Pwto 0.2 to 0.5.

In a further preferred aspect of the present invention, the ratio of theshortest blank region interval to a linear recording velocity is setequal to or smaller than 20 nsec.

In a further preferred aspect of the present invention, the ratio Pb1/Pwof the first bottom power Pb1 to the recording power Pw is set to 0.3 to0.45.

In a preferred aspect of the present invention, the pulse whose level isset to a level corresponding to the recording level is constituted bydivided pulses of a number corresponding to a length of the recordingmark.

In a further preferred aspect of the present invention, the power of thelaser beam is modulated in accordance with a pulse train patternincluding a pulse whose level to set to a level corresponding to asecond bottom power lower than the first bottom power after the pulsewhose level is set to a level corresponding to the recording level.

In a preferred aspect of the present invention, the first bottom powerand the recording power are set so that AH is larger than AL where AL isa ratio of the first bottom power to the recording power when data areto be recorded at a first linear recording velocity and AH is a ratio ofthe first bottom power to the recording power when data are to berecorded at a second linear recording velocity higher than the firstlinear recording velocity.

In a further preferred aspect of the present invention, the first bottompower and the recording power are set so that AH is larger than 1.5*ALand smaller than 5.0*AL.

In a further preferred aspect of the present invention, the first bottompower and the recording power are set so that AH is larger than 2.5*ALand smaller than 4.0*AL.

In a further preferred aspect of the present invention, the first linearrecording velocity is set equal to or higher than 5 m/sec and the secondlinear recording velocity is set equal to or higher than 10 m/sec.

The above objects of the present invention can be also accomplished by awrite-once type optical recording medium comprising a substrate and atleast one recording layer formed on the substrate and constituted sothat data are recorded therein by projecting a laser beam whose power ismodulated by a pulse train pattern including at least a pulse whoselevel is set to a level corresponding to a recording power and a pulsewhose level is set to a level corresponding to a first bottom powerthereonto and forming at least two recording marks in the at least onerecording layer, the optical recording medium being recorded with datafor setting recording conditions required for modulating the power ofthe laser beam in accordance with the pulse train pattern in which aratio Pb1/Pw of the first bottom power Pb1 to the recording power Pw isset to 0.1 to 0.5.

According to the present invention, since the optical recording mediumis recorded with data for setting recording conditions required formodulating the power of the laser beam in accordance with the pulsetrain pattern in which a ratio Pb1/Pw of the first bottom power Pb1 tothe recording power Pw is set to 0.1 to 0.5, when data are to berecorded in the optical recording medium by projecting the laser beamthereonto, data can be recorded at a high linear recording velocity bysetting the recording power Pw of the laser beam to a low value based onthe data for setting recording conditions.

In a preferred aspect of the present invention, the optical recordingmedium further comprises a light transmission layer, and a firstrecording layer and a second recording layer formed between thesubstrate and the light transmission layer, and is constituted so thatthe at least two recording marks are formed by projecting the laser beamthereonto, thereby mixing an element contained in the first recordinglayer as a primary component and an element contained in the secondrecording layer as a primary component.

In a further preferred aspect of the present invention, the secondrecording layer is formed so as to be in contact with the firstrecording layer.

In the present invention, it is preferable for the first recording layerand the second recording layer to contain different elements as aprimary component and for each of them to contain an element selectedfrom a group consisting of Al, Si, Ge, C, Sn, Au, Zn, Cu, B, Mg, Ti, Mn,Fe, Ga, Zr, Ag and Pt as a primary component.

In a preferred aspect of the present invention, the first recordinglayer contains an element selected from a group consisting of Si, Ge,Sn, Mg, In, Zn, Bi and Al as a primary component, and the secondrecording layer contains Cu as a primary component.

In the present invention, in the case where the first recording layercontains an element selected from a group consisting of Si, Ge, Sn, Mg,In, Zn, Bi and Al as a primary component, and the second recording layercontains Cu as a primary component, the optical recording medium mayinclude one or more recording layers containing an element selected fromthe group consisting of Si, Ge, Sn, Mg, In, Zn, Bi and Al as a primarycomponent or one or more recording layers containing Cu as a primaryelement, in addition to the first recording layer and the secondrecording layer.

In the present invention, it is more preferable for the first recordinglayer to contain an element selected from a group consisting of Ge, Si,Mg, Al and Sn as a primary component.

In the present invention, in the case where the first recording layercontains an element selected from a group consisting of Si, Ge, Sn, Mg,In, Zn, Bi and Al as a primary component, and the second recording layercontains Cu as a primary component, it is preferable that at least onekind of an element selected from the group consisting of Al, Si, Zn, Mg,Au, Sn, Ge, Ag, P, Cr, Fe and Ti is added to the second recording layerand it is more preferable that at least one kind of an element selectedfrom the group consisting of Al, Zn, Sn and Au is added to the secondrecording layer.

In another preferred aspect of the present invention, the firstrecording layer contains an element selected from a group consisting ofSi, Ge, C, Sn, Zn and Cu as a primary component and the second recordinglayer contains Al as a primary component.

In the present invention in the case where the first recording layercontains an element selected from a group consisting of Si, Ge, C, Sn,Zn and Cu as a primary component and the second recording layer containsAl as a primary component, the optical recording medium may include oneor more recording layer containing an element selected from the groupconsisting of Si, Ge, C, Sn, Zn and Cu as a primary component or one ormore recording layer containing Al as a primary component, in additionto the first recording layer and the second recording layer.

In the present invention in the case where the first recording layercontains an element selected from a group consisting of Si, Ge, C, Sn,Zn and Cu as a primary component and the second recording layer containsAl as a primary component, it is preferable that at least one kind of anelement selected from the group consisting of Mg, Au, Ti and Cu is addedto the second recording layer.

In the present invention in the case where the first recording layercontains an element selected from a group consisting of Si, Ge, C, Sn,Zn and Cu as a primary component and the second recording layer containsAl as a primary component, the first recording layer and the secondrecording layer are preferably formed so that the total thicknessthereof is 2 nm to 40 nm, more preferably, 2 nm to 30 nm, mostpreferably, 2 nm to 20 nm.

In a further preferred aspect of the present invention, the firstrecording layer contains an element selected from a group consisting ofSi, Ge, C and Al as a primary component, the second recording layercontains Zn as a primary component and the first recording layer and thesecond recording layer are formed so that the total thickness thereof isequal to or thinner than 30 nm.

In the present invention, in the case where the first recording layercontains an element selected from a group consisting of Si, Ge, C and Alas a primary component and the second recording layer contains Zn as aprimary component, the optical recording medium may include one or morerecording layer containing an element selected from the group consistingof Si, Ge, C and Al as a primary component or one or more recordinglayer containing Zn as a primary component.

In the present invention, in the case where the first recording layercontains an element selected from a group consisting of Si, Ge, C and Alas a primary component and the second recording layer contains Zn as aprimary component, it is preferable for the first recording layer tocontain an element selected from a group consisting of Si, Ge and C as aprimary component.

In the present invention, in the case where the first recording layercontains an element selected from a group consisting of Si, Ge, C and Alas a primary component and the second recording layer contains Zn as aprimary component, the first recording layer and the second recordinglayer are preferably formed so that the total thickness thereof is 2 nmto 30 nm, more preferably, 2 nm to 24 nm, most preferably, 2 nm to 12nm.

In the present invention, in the case where the first recording layercontains an element selected from a group consisting of Si, Ge, C and Alas a primary component and the second recording layer contains Zn as aprimary component, it is preferable that at least one kind of an elementselected from the group consisting of Mg, Cu and Al I added to thesecond recording layer.

In a preferred aspect of the present invention, the light transmissionlayer is formed so as to have a thickness of 10 nm to 300 nm.

The above and other objects and features of the present invention willbecome apparent from the following description made with reference tothe accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic cross-sectional view showing the structure of anoptical recording medium that is a preferred embodiment of the presentinvention.

FIG. 2(a) is a schematic enlarged cross-sectional view of the opticalrecording medium shown in FIG. 1 and

FIG. 2(b) is a schematic enlarged cross-sectional view showing anoptical recording medium after data have been recorded therein.

FIG. 3 is a set of diagrams showing a first pulse train pattern in thecase where the 1.7RLL Modulation Code is employed, wherein FIG. 3(a)shows a pulse train pattern when a 2 T signal is recorded and FIG. 3(b)shows a pulse train pattern when one of a 3 T signal to an 8 T signal isrecorded.

FIG. 4 is a set of diagrams showing a first pulse train pattern in thecase where the 1.7RLL Modulation Code is employed, wherein FIG. 4(a)shows a pulse train pattern when a 2 T signal is recorded and

FIG. 4(b) shows a pulse train pattern when one of a 3 T signal to an 8 Tsignal is recorded.

FIG. 5 is a block diagram showing a data recording and reproducingapparatus that is a preferred embodiment of the present invention.

FIG. 6 is a graph showing the relationship between optimum recordingpower Pw and first bottom power Pb1 in the case where data were recordedat a data transfer rate of about 35 Mbps by modulating the power of alaser beam using a first pulse train pattern having a pulse whose levelwas set to a level corresponding to the optimum recording power Pw,where the optimum recording power Pw was defined as the recording powerPw when jitter was minimum, and the relationship between optimumrecording power Pw and first bottom power Pb1 in the case where datawere recorded at a data transfer rate of about 35 Mbps by modulating thepower of a laser beam using a second pulse train pattern having a pulsewhose level was set to a level corresponding to the optimum recordingpower Pw.

FIG. 7 is a graph showing the relationship between optimum recordingpower Pw and first bottom power Pb1 in the case where data were recordedat a data transfer rate of about 70 Mbps by modulating the power of alaser beam using a first pulse train pattern having a pulse whose levelwas set to a level corresponding to the optimum recording power Pw,where the optimum recording power Pw was defined as the recording powerPw when jitter was minimum, and the relationship between optimumrecording power Pw and first bottom power Pb1 in the case where datawere recorded at a data transfer rate of about 70 Mbps by modulating thepower of a laser beam using a second pulse train pattern having a pulsewhose level was set to a level corresponding to the optimum recordingpower Pw.

FIG. 8 is a graph showing the relationship between C/N ratio of a 2 Tsignal and first bottom power Pb1 in the case where data were recordedat a data transfer rate of about 35 Mbps by modulating the power of alaser beam using a first pulse train pattern having a pulse whose levelwas set to a level corresponding to the optimum recording power Pw andthe relationship between C/N ratio of a 2 T signal and first bottompower Pb1 in the case where data were recorded at a data transfer rateof about 35 Mbps by modulating the power of a laser beam using a secondpulse train pattern having a pulse whose level was set to a levelcorresponding to the optimum recording power Pw.

FIG. 9 is a diagram showing a typical pulse train pattern used forrecording data in a CD-R including a recording layer containing anorganic dye.

FIG. 10 is a diagram showing a typical pulse train pattern (basic pulsetrain pattern) used for recording data in a DVD-R including a recordinglayer containing an organic dye.

DESCRIPTION OF THE INVENTION

Preferred embodiments of the present invention will now be describedwith reference to accompanying drawings.

FIG. 1 is a schematic cross-sectional view showing the structure of anoptical recording medium that is a preferred embodiment of the presentinvention.

As shown in FIG. 1, the optical recording medium 10 according to thisembodiment is constituted as a write-once type optical recording mediumand includes a substrate 11, a reflective layer 12 formed on the surfaceof the substrate 11, a second dielectric layer 13 formed on the surfaceof the reflective layer 12, a second recording layer 32 formed on thesurface of the second dielectric layer 13, a first recording layer 31formed on the surface of the second recording layer 32, a firstdielectric layer 15 formed on the surface of the first recording layer31 and a light transmission layer 16 formed on the surface of the firstdielectric layer 15.

As shown in FIG. 1, a center hole is formed at a center portion of theoptical recording medium 10.

In this embodiment, as shown in FIG. 1, a laser beam L10 is projectedonto the surface of the light transmission layer 16, thereby recordingdata in the optical recording medium 10 or reproducing data from theoptical recording medium 10.

The substrate 11 serves as a support for ensuring mechanical strengthrequired for the optical recording medium 10.

The material used to form the substrate 11 is not particularly limitedinsofar as the substrate 11 can serve as the support of the opticalrecording medium 10. The substrate 11 can be formed of glass, ceramic,resin or the like. Among these, resin is preferably used for forming thesubstrate 11 since resin can be easily shaped. Illustrative examples ofresins suitable for forming the substrate 40 include polycarbonateresin, acrylic resin, epoxy resin, polystyrene resin, polyethyleneresin, polypropylene resin, silicone resin, fluoropolymers,acrylonitrile butadiene styrene resin, urethane resin and the like.Among these, polycarbonate resin is most preferably used for forming thesubstrate 11 from the viewpoint of easy processing, opticalcharacteristics and the like.

In this embodiment, the substrate 11 has a thickness of about 1.1 mm.

The shape of the substrate 11 is not particularly limited but isnormally disk-like, card-like or sheet-like.

As shown in FIG. 1, grooves 11 a and lands 11 b are alternately formedon the surface of the substrate 11. The grooves 11 a and/or lands 11 bserve as a guide track for the laser beam L10 when data are to berecorded or when data are to be reproduced.

The reflective layer 12 serves to reflect the laser beam L10 enteringthrough the light transmission layer 16 so as to emit it from the lighttransmission layer 16.

The thickness of the reflective layer 12 is not particularly limited butis preferably from 10 nm to 300 nm, more preferably from 20 nm to 200nm.

The material used to form the reflective layer 12 is not particularlylimited insofar as it can reflect a laser beam, and the reflective layer12 can be formed of Mg, Al, Ti, Cr, Fe, Co, Ni, Cu, Zn, Ge, Ag, Pt, Auand the like. Among these materials, it is preferable to form thereflective layer 12 of a metal material having a high reflectivity, suchas Al, Au, Ag, Cu or alloy containing at least one of these metals, suchas alloy of Al and Ti.

The reflective layer 12 is provided in order to increase the differencein reflection coefficient between a recorded region and an unrecordedregion by a multiple interference effect when the laser beam L10 is usedto optically reproduce data from the first recording layer 31 and thesecond recording layer 32, thereby obtaining a higher reproduced signal(C/N ratio).

The first dielectric layer 15 and the second dielectric layer 13 serveto protect the first recording layer 31 and the second recording layer32. Degradation of optically recorded data can be prevented over a longperiod by the first dielectric layer 15 and the second dielectric layer13. Further, since the second dielectric layer 13 also serves to preventthe substrate 11 and the like from being deformed by heat, it ispossible to effectively prevent jitter and the like from becoming worsedue to the deformation of the substrate 11 and the like.

The dielectric material used to form the first dielectric layer 15 andthe second dielectric layer 13 is not particularly limited insofar as itis transparent and the first dielectric layer 15 and the seconddielectric layer 13 can be formed of a dielectric material containingoxide, sulfide, nitride or a combination thereof, for example, as aprimary component. More specifically, in order to prevent the substrate11 and the like from being deformed by heat and thus protect the firstrecording layer 31 and the second recording layer 32, it is preferablefor the first dielectric layer 15 and the second dielectric layer 13 tocontain at least one kind of dielectric material selected from the groupconsisting of Al₂O₃, AlN, ZnO, ZnS, GeN, GeCrN, CeO, SiO, SiO₂, SiN andSiC as a primary component and it is more preferable for the firstdielectric layer 15 and the second dielectric layer 13 to containZnS.SiO₂ as a primary component.

The first dielectric layer 15 and the second dielectric layer 13 may beformed of the same dielectric material or of different dielectricmaterials. Moreover, at least one of the first dielectric layer 15 andthe second dielectric layer 13 may have a multi-layered structureincluding a plurality of dielectric films.

In this specification, the statement that a dielectric layer contains acertain dielectric material as a primary component means that thedielectric material is maximum among dielectric materials contained inthe dielectric layer. ZnS.SiO₂ means a mixture of ZnS and SiO₂.

The thickness of the first dielectric layer 15 and the second dielectriclayer 13 is not particularly limited but is preferably from 3 nm to 200nm. If the first dielectric layer 15 or the second dielectric layer 13is thinner than 3 nm, it is difficult to obtain the above-describedadvantages. On the other hand, if the first dielectric layer 15 or thesecond dielectric layer 13 is thicker than 200 nm, it takes a long timeto form the first dielectric layers 15 and the second dielectric layers13, thereby lowering the productivity of the optical recording medium10, and cracks may be generated in the optical recording medium 10 owingto stress present in the first dielectric layers 15 and/or the seconddielectric layer 13.

The first recording layer 31 and the second recording layer 32 areadapted for recording data therein. In this embodiment, the firstrecording layer 31 is disposed on the side of the light transmissionlayer 16 and the second recording layer 32 is disposed on the side ofthe substrate 11.

In this embodiment, the first recording layer 31 contains an elementselected from the group consisting of Si, Ge, Sn, Mg, In, Zn, Bi and Alas a primary component and the second recording layer 32 contains Cu asa primary component.

It is possible to improve the long term storage reliability of anoptical recording medium 10 by proving the first recording layer 31containing an element selected from the group consisting of Si, Ge, Sn,Mg, In, Zn, Bi and Al as a primary component and the second recordinglayer 32 containing Cu as a primary component in this manner.

Further, these elements apply only light load to the environment andthere is no risk of the global atmosphere being damaged.

In order to thoroughly improve the C/N ratio of the reproduced signal,it is particularly preferable for the first recording layer 31 tocontain an element selected from the group consisting of Ge, Si, Mg, Aland Sn as a primary component and is particularly preferable for the tocontain Si as a primary component.

Cu contained in the second recording layer 32 as a primary componentquickly mixes with the element contained in the first recording layer 31when irradiated with a laser beam L10, thereby enabling data to bequickly recorded in the first recording layer 31 and the secondrecording layer 32.

In order to improve the recording sensitivity of the first recordinglayer 31, it is preferable for the first recording layer 31 to be addedwith at least one kind of an element selected from the group consistingof Mg, Al, Cu, Ag and Au.

In order to improve the storage reliability and the recordingsensitivity of the second recording layer 32, it is preferable for thesecond recording layer 32 to be added with at least one kind of anelement selected from the group consisting of Al, Si, Zn, Mg, Au, Sn,Ge, Ag, P, Cr, Fe and Ti.

The total thickness of the first recording layer 31 and the secondrecording layer 32 is not particularly limited but the surfacesmoothness of the first recording layer 31 irradiated with the laserbeam L10 becomes worse as the total thickness of the first recordinglayer 31 and the second recording layer 32 becomes thicker. As a result,the noise level of the reproduced signal becomes higher and therecording sensitivity is lowered. On the other hand, in the case wherethe total thickness of the first recording layer 31 and the secondrecording layer 32 is too small, the change in reflection coefficientbetween before and after irradiation with the laser beam L10 is small,so that a reproduced signal having high strength (C/N ratio) cannot beobtained. Moreover, it becomes difficult to control the thickness of thefirst recording layer 31 and the second recording layer 32.

Therefore, in this embodiment, the first recording layer 31 and thesecond recording layer 32 are formed so that the total thickness thereofis from 2 nm to 40 nm. In order to obtain a reproduced signal havinghigher strength (C/N ratio) and further decrease the noise level of thereproduced signal, the total thickness of the first recording layer 31and the second recording layer 32 is preferably from 2 nm to 20 nm andmore preferably 2 nm to 10 nm.

The individual thicknesses of the first recording layer 31 and thesecond recording layer 32 are not particularly limited but in order toconsiderably improve the recording sensitivity and greatly increase thechange in reflection coefficient between before and after irradiationwith the laser beam L10, the thickness of the first recording layer 31is preferably from 1 nm to 30 nm and the thickness of the secondrecording layer 32 is preferably from 1 nm to 30 nm. Further, it ispreferable to define the ratio of the thickness of the first recordinglayer 31 to the thickness of the second recording layer 32 (thickness offirst recording layer 31/thickness of second recording layer 32) to befrom 0.2 to 5.0.

The light transmission layer 16 serves to transmit a laser beam L10 andpreferably has a thickness of 10 μm to 300 μm. More preferably, thelight transmission layer 16 has a thickness of 50 μm to 150 μm.

The material used to form the light transmission layer 16 is notparticularly limited but in the case where the light transmission layer16 is to be formed by the spin coating process or the like, ultravioletray curable resin, electron beam curable resin or the like is preferablyused. More preferably, the light transmission layer 16 is formed ofultraviolet ray curable resin.

The light transmission layer 16 may be formed by adhering a sheet madeof light transmittable resin to the surface of the first dielectriclayer 15 using an adhesive agent.

The optical recording medium 10 having the above-described configurationcan, for example, be fabricated in the following manner.

The reflective layer 12 is first formed on the surface of the substrate11 formed with the grooves 11 a and lands 11 b.

The reflective layer 12 can be formed by a gas phase growth processusing chemical species containing elements for forming the reflectivelayer 12. Illustrative examples of the gas phase growth processesinclude vacuum deposition process, sputtering process and the like.

The second dielectric layer 13 is then formed on surface of thereflective layer 12.

The second dielectric layer 13 can be also formed by a gas phase growthprocess using chemical species containing elements for forming thesecond dielectric layer 13. Illustrative examples of the gas phasegrowth processes include vacuum deposition process, sputtering processand the like.

The second recording layer 32 is further formed on the second dielectriclayer 13. The second recording layer 32 can be also formed by a gasphase growth process using chemical species containing elements forforming the second recording layer 32.

The first recording layer 31 is then formed on the second recordinglayer 32. The first recording layer 31 can be also formed by a gas phasegrowth process using chemical species containing elements for formingthe first recording layer 31.

The first dielectric layer 15 is then formed on the first recordinglayer 31. The first dielectric layer 15 can be also formed by a gasphase growth process using chemical species containing elements forforming the first dielectric layer 15.

Finally, the light transmission layer 16 is formed on the firstdielectric layer 15. The light transmission layer 16 can be formed, forexample, by applying an acrylic ultraviolet ray curable resin or epoxyultraviolet ray curable resin adjusted to an appropriate viscosity ontothe surface of the second dielectric layer 15 by spin coating to form acoating layer and irradiating the coating layer with ultraviolet rays tocure the coating layer.

Thus, the optical recording medium 10 was fabricated.

Data are recorded in the optical recording medium 10 of theabove-described configuration, in the following manner, for example.

As shown in FIG. 1 and 2(a), the first recording layer 31 and the secondrecording layer 32 are first irradiated via the light transmission layer16 with a laser beam L10 having predetermined power.

In order to record data with high recording density, it is preferable toproject a laser beam L10 having a wavelength λ of 450 nm or shorter ontothe optical recording medium 10 via an objective lens (not shown) havinga numerical aperture NA of 0.7 or more and it is more preferable thatλ/NA be equal to or smaller than 640 nm. In such a case, the spotdiameter of the laser beam L10 on the surface of the first recordinglayer 31 becomes equal to or smaller than 0.65 μm.

In this embodiment, a laser beam L10 having a wavelength λ of 405 nm iscondensed onto the optical recording medium 10 via an objective lenshaving a numerical aperture NA of 0.85 so that the spot diameter of thelaser beam L10 on the surface of the first recording layer 31 becomesabout 0.43 μm.

As a result, the element contained in the first recording layer 31 as aprimary component and the element contained in the second recordinglayer 32 as a primary component mix with each other and as shown in FIG.2(b), a recording mark M composed of a mixture of the primary componentelement of the first recording layer 31 and the primary componentelement of the second recording layer 32 is formed.

When the primary component elements of the first recording layers 31 and32 are mixed, the reflection coefficient of the region markedly changes.Since the reflection coefficient of the thus formed recording mark M istherefore greatly different from that of the region surrounding themixed region M, it is possible to obtain a high reproduced signal (C/Nratio) when optically recorded information is reproduced.

When the laser beam L10 is projected, the first recording layer 31 andthe second recording layer 32 are heated by the laser beam L10. In thisembodiment, however, the first dielectric layer 15 and the seconddielectric layer 13 are disposed outward of the first recording layer 31and the second recording layer 32. Deformation of the substrate 11 andthe light transmission layer 16 by heat is therefore effectivelyprevented.

FIG. 3 is a set of diagrams showing a first pulse train pattern in thecase where the 1.7RLL Modulation Code is employed, wherein FIG. 3(a)shows a pulse train pattern when a 2 T signal is recorded and FIG. 3(b)shows a pulse train pattern when one of a 3 T signal to an 8 T signal isrecorded.

The first pulse train pattern is a pattern for modulating the power of alaser beam L10 suitable for the case of forming a recording mark M usinga lower recording power Pw and is preferably employed in the case ofincreasing the linear recording velocity to or higher than 5 m/sec andrecording data at a high data transfer rate.

As shown in FIGS. 3(a) and 3(b), in the first pulse train pattern, arecording pulse for forming a recording mark M is divided into (n−1)divided pulses and the power of a laser beam L10 is set to a recordingpower Pw at the peak of each of the divided pulses and set to a firstbottom power Pb1 higher than a reproducing power Pr of a laser beam L10used for reproducing data at other portions of the pulse. Morespecifically, the first pulse train pattern is constituted by increasingthe bottom power Pb in the basic pulse train pattern shown in FIG. 10from a level substantially equal to the reproducing power Pr to thefirst bottom power Pb1 higher than the reproducing power Pr.

The recording power Pw is set to a high level such that the elementcontained in the first recording layer 31 as a primary component and theelement contained in the second recording layer 32 as a primarycomponent can be heated and mixed to form a record mark M when a laserbeam having the recording power Pw is projected onto the opticalrecording medium 10. On the other hand, the first bottom power Pb1 isset to a low level such that it is higher than the reproducing power Prbut the element contained in the first recording layer 31 as a primarycomponent and the element contained in the second recording layer 32 asa primary component cannot substantially be mixed when a laser beamhaving the first bottom power Pb1 is projected onto the opticalrecording medium 10.

It is preferable for the ratio Pb1/Pw of the first bottom power Pb1 tothe recording power Pw to be 0.1 to 0.5, and when data are to berecorded at a linear recording velocity equal to or higher than 10m/sec, it is preferable for the ratio Pb1/Pw of the first bottom powerPb1 to the recording power Pw to be 0.2 to 0.5 and is more preferablefor it to be 0.3 to 0.45.

In the case where it is assumed that the ratio Pb1/Pw of the firstbottom power Pb1 to the recording power Pw when data are to be recordedat a linear velocity VL is AL and the ratio Pb1/Pw of the first bottompower Pb1 to the recording power Pw when data are to be recorded at alinear velocity VH is AH, it is preferable to set the first bottom powerPb1 and the recording power Pw so that AH is larger than AL, is morepreferable to set it so that AH is larger than 1.5*AL and smaller than5.0*AL and is most preferable to set it so that AH is larger than 2.5*ALand smaller than 4.0*AL.

In the case where the first pulse train pattern is constituted in thismanner, the heating of a region where a recording mark M is to be formedby a laser beam whose power is set to the recording power Pw isaugmented by a laser beam whose power is set to the first bottom powerPb1, thereby facilitating the formation of a recording mark M. On theother hand, the element contained in the first recording layer 31 as aprimary component and the element contained in the second recordinglayer 32 as a primary component are prevented from mixing with eachother at a blank region between neighboring recording marks M andforming a recording mark M.

Therefore, in the case where the power of a laser beam L10 is modulatedusing the first pulse train pattern, thereby recording data in theoptical recording medium 10, a recording mark M can be formed using alaser beam L10 having a lower recording power Pw and it is thereforepossible to achieve a high transfer rate by increasing the linearrecording velocity to or higher than 5 m/sec.

FIG. 4 is a set of diagrams showing a first pulse train pattern in thecase where the 1.7RLL Modulation Code is employed, wherein FIG. 4(a)shows a pulse train pattern when a 2 T signal is recorded and FIG. 4(b)shows a pulse train pattern when one of a 3 T signal to an 8 T signal isrecorded.

The second pulse train pattern is a pattern for modulating a laser beamL10 which is suitable for forming a recording mark M by a laser beam L10having a lower recording power Pw and is preferably selected in the casewhere it is necessary to cool a downstream edge portion of a recordingmark M with respect to the moving direction of a laser beam L10(hereinafter referred to as “a rear edge portion of a recording mark”).

As shown in FIGS. 4(a) and 4(b), in the second pulse train pattern, arecording pulse for forming a recording mark M is divided into (n−1)divided pulses and the power of a laser beam L10 is set to a recordingpower Pw at the peak of each of the divided pulses, set to a secondbottom power Pb2 immediately before a first divided pulse and set to afirst bottom power Pb1 at other portions of the pulse. As shown in FIG.4, the first bottom power Pb1 and the second bottom power Pb2 aredetermined so that the first bottom power Pb1 is higher than the secondbottom power Pb2 and the second bottom power Pb2 is determined to besubstantially equal to a reproducing power Pr or close thereto.

Therefore, the second pulse train pattern is constituted by inserting acooling interval Tcl at which the power of a laser beam L10 is set tothe second bottom power Pb2 into a portion immediately after a lastdivided pulse in the basic pulse train pattern shown in FIG. 10 andincreasing the bottom power Pb in the basic pulse train pattern shown inFIG. 10 to the first bottom power Pb1 substantially equal to or higherthan the reproducing power Pr.

In the second pulse train pattern, the recording power Pw is set to ahigh level at which the element contained in the first recording layer31 as a primary component and the element contained in the secondrecording layer 32 as a primary component can be heated and mixed toform a record mark M when a laser beam having the recording power Pw isprojected onto the optical recording medium 10. On the other hand, thefirst bottom power Pb1 is set to a low level such that it is higher thanthe reproducing power Pr but the element contained in the firstrecording layer 31 as a primary component and the element contained inthe second recording layer 32 as a primary component cannotsubstantially be mixed when a laser beam having the first bottom powerPb1 is projected onto the optical recording medium 10.

The ratio Pb1/Pw of the first bottom power Pb1 to the recording power Pwis set similarly in the first pulse train pattern.

In the case where the second pulse train pattern is constituted in thismanner, the heating of a region where a recording mark M is to be formedby a laser beam whose power is set to the recording power Pw isaugmented by a laser beam whose power is set to the first bottom powerPb1, thereby facilitating the formation of a recording mark M. On theother hand, the element contained in the first recording layer 31 as aprimary component and the element contained in the second recordinglayer 32 as a primary component are prevented from mixing with eachother at a blank region between neighboring recording marks M andforming a recording mark M.

Therefore, in the case where the power of a laser beam L10 is modulatedusing the second pulse train pattern, thereby recording data in theoptical recording medium 10, a recording mark M can be formed using alaser beam L10 having a lower recording power Pw and it is thereforepossible to achieve a high transfer rate by increasing the linearrecording velocity to or higher than 5 m/sec.

Further, in the second pulse train pattern, since a cooling interval Tclat which the power of a laser beam L10 is set to the second bottom powerPb2 is inserted into a portion immediately after a last divided pulse,the rear edge portion of a recording mark M heated by a laser beam L10having the recording power Pw projected for forming the recording mark Mcan be effectively cooled, thereby preventing the element contained inthe first recording layer 31 as a primary component and the elementcontained in the second recording layer 32 as a primary component frommixing with each other at a region downstream of the rear edge portionof the recording mark M with respect to the moving direction of thelaser beam L10. It is therefore possible to effectively prevent the rearedge portion of a recording mark M from being shifted and control thelength and width of a recording mark M in a desired manner.

According to this embodiment, since a recording pulse of a laser beamL10 for forming a recording mark M is divided into (n−a) divided pulseswhere a is 0, 1 or 2 and it is preferable to set a to 2 in the 8/16Modulation Code and set a to 1 in 1,7RLL Modulation Code and the firstbottom power Pb1 and the second bottom power Pb2 are determined so thatthe ratio Pb1/Pb2 of the first bottom power Pb1 to the second bottompower Pb2 is 0.1 to 0.5, data can be recorded in the optical recordingmedium 10 using a laser beam L10 having a low recording power Pw. It istherefore possible to employ a relatively inexpensive semiconductorlaser beam having a low output even in the case data are to be recordedat a linear recording velocity equal to or higher than 5 m/sec.

FIG. 5 is a block diagram showing a data recording apparatus that is apreferred embodiment of the present invention.

As shown in FIG. 5, a data recording apparatus 100 includes a spindlemotor 52 for rotating the optical recording medium 10, a head 53 forprojecting a laser beam onto the optical recording medium 10 andreceiving the light reflected by the optical recording medium 10, acontroller 54 for controlling the operation of the spindle motor 52 andthe head 53, a laser drive circuit 55 for feeding a laser drive signalto the head 53, and a lens drive circuit 56 for feeding a lens drivesignal to the optical head 53.

As shown in FIG. 5, the controller 54 includes a focus servo trackingcircuit 57, a tracking servo circuit 58 and a laser control circuit 59.

When the focus servo tracking circuit 57 is activated, a laser beam L10is focused onto the first recording layer 51 of the rotating opticalrecording medium 10 and when the tracking servo circuit 58 is activated,the spot of the laser beam L10 automatically follows the track of theoptical recording medium 10.

As shown in FIG. 5, each of the focus servo tracking circuit 57 and thetracking servo circuit 58 has an auto-gain control function forautomatically adjusting the focus gain and an auto-gain control functionfor automatically adjusting the tracking gain.

Further, the laser control circuit 59 is adapted to generate a laserdrive signal to be supplied by the laser drive circuit 55.

In this embodiment, data for identifying the above described first pulsetrain pattern or the second pulse train pattern are recorded in theoptical recording medium 10 together with data for identifying variousrecording conditions, such as a linear recording velocity necessary forrecording data, as data for setting recording conditions in the form ofwobbles or pre-pits.

Therefore, the laser control circuit 59 reads data for setting recordingconditions recorded in the optical recording medium 10 prior torecording data in the optical recording medium 10, selects the firstpulse train pattern or the second pulse train pattern based on the thusread data for setting recording conditions to generate a laser drivesignal and causes the laser drive circuit 55 to output it to the head53.

Thus, data are recorded in the optical recording medium 10 in accordancewith the desired recording strategy.

According to this embodiment, the optical recording medium 10 isrecorded with data for identifying the first pulse train pattern or thesecond pulse train pattern together with data for identifying variousrecording conditions, such as a linear recording velocity necessary forrecording data, as data for setting recording conditions and prior torecording data in the optical recording medium 10, the laser controlcircuit 59 reads data for setting recording conditions recorded in theoptical recording medium 10, selects the first pulse train pattern orthe second pulse train pattern based on the thus read data for settingrecording conditions to generate a laser drive signal and control thehead 53 for projecting a laser beam onto the optical recording medium10. Therefore, it is possible to record data in accordance with thedesired recording strategy.

WORKING EXAMPLES AND A COMPARATIVE EXAMPLE

Hereinafter, working examples and a comparative example will be set outin order to further clarify the advantages of the present invention.

Fabrication an Optical Recording Medium

An optical recording medium having the same configuration as that of theoptical recording medium 1 shown in FIG. 1 was fabricated in thefollowing manner.

A polycarbonate substrate having a thickness of 1.1 mm and a diameter of120 mm was first set on a sputtering apparatus. Then, a reflective layercontaining a mixture of Ag, Pd and Cu and having a thickness of 100 nm,a second dielectric layer containing a mixture of ZnS and SiO₂ andhaving a thickness of 30 nm, a second recording layer containing Cu as aprimary component and having a thickness of 5 nm, a first recordinglayer containing Si as a primary component and having a thickness of 5nm and a first dielectric layer containing the mixture of ZnS and SiO₂and having a thickness of 25 nm were sequentially formed on thepolycarbonate substrate using the sputtering process.

The mole ratio of ZnS to SiO₂ in the mixture of ZnS and SiO₂ containedin the first dielectric layer and the second dielectric layer was 80:20.

Further, the first dielectric layer was coated using the spin coatingmethod with an acrylic ultraviolet ray curable resin to form a coatinglayer and the coating layer was irradiated with ultraviolet rays,thereby curing the acrylic ultraviolet ray curable resin to form a lighttransmission layer having a thickness of 100 μm.

WORKING EXAMPLE 1

The thus fabricated optical recording medium was set in an opticalrecording medium evaluation apparatus “DDU1000” (Product Name)manufactured by Pulstec Industrial Co., Ltd. Then, a blue laser beamhaving a wavelength of 405 nm was employed as the laser beam forrecording data and the laser beam was condensed onto the opticalrecording medium via the light transmission layer using an objectivelens whose numerical aperture was 0.85, and data were recorded thereinunder the following recording signal conditions.

Modulation Code: (1.7) RLL

Channel Bit Length: 0.12 μm

Linear Recording Velocity: 5.3 m/sec

Channel Clock: 66 MHz

Recording Signal: random signal including a 2 T signal to an 8 T signalin no particular order

Data were recorded by modulating a laser beam in accordance with thefirst pulse train pattern including (n−1) divided pulses as a recordingpulse wherein n was an integer of 2 to 8, varying the first bottom powerPb1 between 0.5 mW, 1.0 mW, 1.5 mW and 2.0 Mw and varying the recordingpower Pw.

Under these recording conditions, the data transfer rate was about 35Mbps when the format efficiency was 80% and the ratio of the shortestblank region interval to the linear recording velocity (shortest blankregion interval/linear recording velocity) was 30.4 nsec.

Further, data recorded in the optical recording medium were reproducedusing the above mentioned optical recording medium evaluation apparatus.Then, jitter of the reproduced signals was measured using an optimumrecording power Pw determined as the recording power Pw when jitter wasminimum and the relationship between the optimum recording power Pw andthe first bottom power Pb1 was determined. When data were reproduced, alaser beam having a wavelength of 405 nm and an objective lens whosenumerical aperture (NA) was 0.85 were employed.

WORKING EXAMPLE 2

Data were recorded in the optical recording medium similarly to inWorking Example 1 except that the following recording conditions wereemployed. Then, the optimum recording power Pw was determined as thepower of a laser beam when jitter was minimum and the relationshipbetween the optimum recording power Pw and the first bottom power Pb1was determined.

Modulation Code: (1.7) RLL

Channel Bit Length: 0.12 μm

Linear Recording Velocity: 10.6 m/sec

Channel Clock: 132 MHz

Recording Signal: random signal including a 2 T signal to an 8 T signalin no particular order

Under these recording conditions, the data transfer rate was about 70Mbps when the format efficiency was 80% and the ratio of the shortestblank region interval to the linear recording velocity (shortest blankregion interval/linear recording velocity) was 15.2 nsec.

The results of the measurement in Working Examples 1 and 2 are shown inFIG. 6.

As shown in FIG. 6, it was found that when data were recorded bymodulating the power of the laser beam in accordance with the firstpulse train pattern, the level of the optimum recording power Pw becamelower as the first bottom power Pb1 was set to a higher level and thatwhen the data transfer rate was about 70 Mbps, the level of the optimumrecording power Pw was markedly lowered in accordance with the increasein the level of the first bottom power Pb1.

Therefore, it was found that in the case where the linear recordingvelocity was high and the data transfer rate was high, it was effectiveto record data by modulating the power of the laser beam in accordancewith the first pulse train pattern.

Further, it was found that data could be recorded at different linearrecording velocities by setting the first bottom power Pb1 of the laserbeam to a higher level as the linear recording velocity was higher,while maintaining the recording power Pw of the laser beam at the samelevel or substantially the same level. More specifically, it was foundthat it was possible to prevent jitter from becoming worse by settingthe first bottom power Pb1 and the recording power Pw of a laser beam to0.5 mW and 4.6 mW, respectively, and recording data in the case wheredata were recorded at a data transfer rate of about 35 Mbps and settingthe first bottom power Pb1 and the recording power Pw of a laser beam to2.0 mW and 4.8 mW, respectively, and recording data in the case wheredata were recorded at a data transfer rate of about 70 Mbps, and thatdata could be recorded using a relatively inexpensive semiconductorlaser having a maximum output of 5 mW.

WORKING EXAMPLE 3

Data were recorded in the optical recording medium similarly to inWorking Examples 1 and 2 except that the power of a laser beam wasmodulated in accordance with the second pulse train pattern. Then, theoptimum recording power Pw was determined as the power of a laser beamwhen jitter was minimum and the relationship between the optimumrecording power Pw and the first bottom power Pb1 was determined.

Here, the length of the cooling interval Tcl was set to 1 T and thesecond bottom power Pb2 was set to 0.1 mW.

The results of the measurement are shown in FIG. 7.

As shown in FIG. 7, it was found that when data were recorded bymodulating the power of the laser beam in accordance with the secondpulse train pattern, the level of the optimum recording power Pw becamelower as the first bottom power Pb1 was set to a higher level and thatwhen the data transfer rate was about 70 Mbps, the level of the optimumrecording power Pw was markedly lowered in accordance with the increasein the level of the first bottom power Pb1.

Therefore, it was found that in the case where the linear recordingvelocity was high and the data transfer rate was high, it was effectiveto record data by modulating the power of the laser beam in accordancewith the second pulse train pattern.

Further, it was found that in the case where the power of a laser beamwas modulated in accordance with the second pulse train pattern and datawere recorded, data could be recorded at different linear recordingvelocities by setting the first bottom power Pb1 of the laser beam to ahigher level as the linear recording velocity was higher, whilemaintaining the recording power Pw of the laser beam at the same levelor substantially the same level. More specifically, it was found that itwas possible to prevent jitter from becoming worse by setting the firstbottom power Pb1 and the recording power Pw of a laser beam to 0.5 mWand 4.6 mW, respectively, and recording data in the case where data wererecorded at a data transfer rate of about 35 Mbps and setting the firstbottom power Pb1 and the recording power Pw of a laser beam to 2.0 mWand 6.0 mW, respectively, and recording data in the case where data wererecorded at a data transfer rate of about 70 Mbps, and that data couldbe recorded using a relatively inexpensive semiconductor laser havingthe maximum output of 6 mW.

Furthermore, as shown in FIGS. 6 and 7, it was found that the phenomenonof the optimum recording power Pw of a laser beam becoming lower as thefirst bottom power Pb1 was set to a higher level was more pronounced inthe case of modulating the power of a laser beam in accordance with thefirst pulse train pattern, thereby recording data, than in the case ofmodulating the power of a laser beam in accordance with the second pulsetrain pattern, thereby recording data. It is reasonable to assume thatthis was because, unlike the second pulse train pattern, the first pulsetrain pattern did not include the cooling interval Tcl and the heatingaugmentation effect by the first bottom power Pb1 was higher in the caseof using the first pulse train pattern than in the case of using thesecond pulse train pattern.

WORKING EXAMPLE 4

The power of a laser beam was modulated in accordance with the firstpulse train pattern and the second pulse train pattern and data wererecorded in the optical recording medium under the same recordingconditions as those in Working Example 1. Then, data recorded in theoptical recording medium were reproduced and the relationship betweenthe first bottom power Pb1 and a C/N ratio of the 2 T signal wasdetermined.

Here, the recording power Pw of the laser beam was set to an optimumrecording power Pw at which jitter was minimum, the cooling interval Tclwas set to 1 T and the second bottom power Pb2 was set to 0.1 mW.

The results of the measurement are shown in FIG. 7.

As shown in FIG. 8, it was found that in the case where the power of alaser beam was modulated in accordance with the first pulse trainpattern including no cooling interval Tcl, thereby recording data, theC/N ratio of the 2 T signal decreased as the first bottom power Pb1 wasincreased but that in the case where the power of a laser beam wasmodulated in accordance with the second pulse train pattern, therebyrecording data, the C/N ratio of the 2 T signal did not substantiallydecrease even when the first bottom power Pb1 was increased.

It is reasonable to assume that the reason for these findings is asfollows. Specifically, since the cooling interval Tcl at which the powerof a laser beam was set to the second bottom power Pb2 was inserted intoa portion immediately after a last divided pulse in the second pulsetrain pattern, the rear edge portion of a recording mark M heated by alaser beam whose power was set to the recording power Pw projected forforming the recording mark M was effectively cooled and the elementcontained in the first recording layer as a primary component and theelement contained in the second recording layer as a primary componentwere prevented from mixing with each other. Therefore, it was possibleto effectively prevent the rear edge portion of the recording mark Mfrom being shifted and the length of the recording mark M was controlledin a desired manner.

The present invention has thus been shown and described with referenceto a specific embodiment and Working Examples. However, it should benoted that the present invention is in no way limited to the details ofthe described arrangements but changes and modifications may be madewithout departing from the scope of the appended claims.

For example, in the above described embodiment and Working Examples,although the first recording layer 31 and the second recording layer 32are formed in contact with each other, it is not absolutely necessary toform the first recording layer 31 and the second recording layer 32 incontact with each other but it is sufficient for the second recordinglayer 32 to be so located in the vicinity of the first recording layer31 as to enable formation of a mixed region including the primarycomponent element of the first recording layer 31 and the primarycomponent element of the second recording layer 32 when the region isirradiated with a laser beam. Further, one or more other layers such asa dielectric layer may be interposed between the first recording layer31 and the second recording layer 32.

Further, in the above described embodiment, although the first recordinglayer 31 contains an element selected from the group consisting of Si,Ge, Sn, Mg, In, Zn, Bi and Al as a primary component and the secondrecording layer 32 contains Cu as a primary component, it is notabsolutely necessary for the first recording layer 31 to contain anelement selected from the group consisting of Si, Ge, Sn, Mg, In, Zn, Biand Al as a primary component and for the second recording layer 32 tocontain Cu as a primary component and the first recording layer 31 maycontain an element selected from the group consisting of Si, Ge, C, Sn,Zn and Cu as a primary component and the second recording layer 32 maycontain Al as a primary component. Further, the first recording layer 31may contain an element selected from the group consisting of Si, Ge, Cand Al as a primary component and the second recording layer 32 maycontain Zn as a primary component. Moreover, it is sufficient for thefirst recording layer 31 and the second recording layer 32 to containdifferent elements from each other and contain an element selected fromthe group consisting of Al, Si, Ge, C, Sn, Au, Zn, Cu, B, Mg, Ti, Mn,Fe, Ga, Zr, Ag and Pt as a primary component.

Furthermore, in the above described embodiment and Working Examples,although the optical recording medium 10 includes the first recordinglayer 31 and the second recording layer 32, the optical recording mediummay include one or more recording layers containing an element selectedfrom the group consisting of Si, Ge, Sn, Mg, In, Zn, Bi and Al as aprimary component or one or more recording layers containing Al as aprimary element, in addition to the first recording layer 31 and thesecond recording layer 32.

Moreover, although the first recording layer 31 is disposed on the sideof the light transmission layer 16 and the second recording layer 32 isdisposed on the side of the substrate 11 in the above describedembodiment and working examples, it is possible to dispose the firstrecording layer 31 on the side of the substrate 11 and the secondrecording layer 32 on the side of the light transmission layer 16.

Further, in the above described embodiment and Working Examples, theoptical recording medium 10 includes the first dielectric layer 15 andthe second dielectric layer 13 and the first recording layer 31 and thesecond recording layer 32 are disposed between the first dielectriclayer 15 and the second dielectric layer 13. However, it is notabsolutely necessary for the optical recording medium 10 to include thefirst dielectric layer 15 and the second dielectric layer 13, i.e., theoptical recording medium 10 may include no dielectric layer. Further,the optical recording medium 10 may include a single dielectric layerand in such case the dielectric layer may be disposed on either the sideof the substrate 11 or the side of the light transmission layer 16 withrespect to the first recording layer 31 and the second recording layer32.

Furthermore, in Working Examples, although the first recording layer 31and the second recording layer 32 are formed so as to have the samethickness in the above described embodiment and working examples, it isnot absolutely necessary to form the first recording layer 31 and thesecond recording layer 32 so as to have the same thickness.

Moreover, in the above described embodiment and Working Examples,although the optical recording medium 10 is provided with the reflectivelayer 12, if the level of reflected light in the recording mark M formedby the mixing an element contained in the first recording layer as aprimary component and Zn contained in the second recording layer as aprimary component and the level of reflected light in regions onto whichthe laser beam was not projected greatly differ from each other, thereflective layer may be omitted.

Further, in the above described embodiment, although all recording marksM are formed by modulating the power of a laser beam in accordance withthe second pulse train pattern in the case where the second pulse trainpattern is to be used, since it is only in the case where the length ofa recording mark M is short that the width of a recording mark M becomesthin and the C/N ratio (carrier/noise ratio) of the signal isconsiderably lowered when the recording power Pw of the laser beam islowered in order to prevent the rear edge portion of a recording mark Mfrom being shifted and the recording mark M from becoming longer than adesired length, it is possible to modulate the power of the laser beamin accordance with the second pulse train pattern only in the case wherea 2 T signal is to be recorded to form the shortest recording mark M andto modulate the power of a laser beam in accordance with the first pulsetrain pattern in the case of recording one of a 3 T signal to an 8 Tsignal to form a recording mark M.

Furthermore, in the embodiment shown in FIG. 6, although the data forsetting recording conditions are recorded in the optical recordingmedium 10 in the form of wobbles or pre-pits, data for setting recordingconditions may be recorded in the first recording layer 31 or the secondrecording layer 32.

Moreover, in the embodiment shown in FIG. 6, although the focus servotracking circuit 57, the tracking servo circuit 58 and the laser controlcircuit 59 are incorporated into the controller 54, it is not absolutelynecessary to incorporate the focus servo tracking circuit 57, thetracking servo circuit 58 and the laser control circuit 59 into thecontroller 54, and the focus servo tracking circuit 57, the trackingservo circuit 58 and the laser control circuit 59 may be providedseparately from the controller 54. Moreover, it is alternativelypossible to install software for accomplishing functions of the focusservo tracking circuit 57, the tracking servo circuit 58 and the lasercontrol circuit 59 in the controller 54.

Further, in the above described embodiment and Working Examples,although the explanation was made as to the case where data are recordedin a next-generation type optical recording medium 10 and where it isrequired to employ a semiconductor laser having a high output, the caseto which the present invention can be applied is not limited to the caseof recording data in a next-generation type optical recording medium butthe present invention can be widely applied to the case of recordingdata in a write-once type optical recording medium other than anext-generation type optical recording medium.

According to the present invention, it is possible to provide a methodfor recording data in an optical recording medium which can record datain a write-once type optical recording medium at a high linear recordingvelocity.

Further, according to the present invention, it is possible to provide amethod for recording data in an optical recording medium which canrecord data in a write-once type optical recording medium using a laserbeam whose recording power is set low.

Furthermore, according to the present invention, it is possible toprovide a method for recording data in an optical recording medium whichcan record data in a write-once type optical recording medium at a highlinear recording velocity using an inexpensive semiconductor laserhaving a low output.

Moreover, according to the present invention, it is possible to providea method for recording data in an optical recording medium which canrecord data in a write-once type optical recording medium including twoor more recording layers at a high linear recording velocity.

Further, according to the present invention, it is possible to providean apparatus for recording data in an optical recording medium which canrecord data in a write-once type optical recording medium at a highlinear recording velocity.

Furthermore, according to the present invention, it is possible toprovide an apparatus for recording data in an optical recording mediumwhich can record data in a write-once type optical recording mediumusing a laser beam whose recording power is set low.

Moreover, according to the present invention, it is possible to providean apparatus for recording data in an optical recording medium which canrecord data in a write-once type optical recording medium at a highlinear recording velocity using an inexpensive semiconductor laserhaving a low output.

Further, according to the present invention, it is possible to providean apparatus for recording data in an optical recording medium which canrecord data in a write-once type optical recording medium including twoor more recording layers at a high linear recording velocity.

Furthermore, according to the present invention, it is possible toprovide an optical recording medium in which data can be recorded at ahigh linear recording velocity.

Moreover, according to the present invention, it is possible to providean optical recording medium in which data can be recorded using a laserbeam whose recording power is set low.

Further, according to the present invention, it is possible to providean optical recording medium in which data can be recorded at a highlinear recording velocity using an inexpensive semiconductor laserhaving a low output.

Furthermore, according to the present invention, it is possible toprovide an optical recording medium including two or more recordinglayers in which data can be recorded at a high linear recordingvelocity.

All of the above U.S. patents, U.S. patent application publications,U.S. patent applications, foreign patents, foreign patent applicationsand non-patent publications referred to in this specification and/orlisted in the Application Data Sheet, are incorporated herein byreference, in their entirety.

From the foregoing it will be appreciated that, although specificembodiments of the invention have been described herein for purposes ofillustration, various modifications may be made without deviating fromthe spirit and scope of the invention. Accordingly, the invention is notlimited except as by the appended claims.

1. A method for recording data in an optical recording medium whereindata are recorded in a write-once type optical recording mediumcomprising a substrate and at least one recording layer formed on thesubstrate by projecting a laser beam whose power is modulated by a pulsetrain pattern including at least a pulse whose level is set to a levelcorresponding to a recording power and a pulse whose level is set to alevel corresponding to a first bottom power onto the at least onerecording layer and forming at least two recording marks in the at leastone recording layer, the method for recording data in an opticalrecording medium comprising a step of setting a ratio Pb1/Pw of a firstbottom power Pb1 to a recording power Pw to 0.1 to 0.5.
 2. The methodfor recording data in an optical recording medium in accordance withclaim 1, wherein data are recorded at a linear recording velocity equalto or higher than 5 m/sec.
 3. The method for recording data in anoptical recording medium in accordance with claim 1, which furthercomprises a light transmission layer, and a first recording layer and asecond recording layer formed between the substrate and the lighttransmission layer, and is constituted so that the at least tworecording marks are formed by projecting the laser beam thereonto,thereby mixing an element contained in the first recording layer as aprimary component and an element contained in the second recording layeras a primary component.
 4. The method for recording data in an opticalrecording medium in accordance with claim 3, wherein the secondrecording layer is formed so as to be in contact with the firstrecording layer.
 5. The method for recording data in an opticalrecording medium in accordance with claim 1, wherein the at least tworecording marks are formed by setting a ratio of the shortest blankregion interval to a linear recording velocity to equal to or smallerthan 40 nsec.
 6. The method for recording data in an optical recordingmedium in accordance with claim 1, wherein data are recorded at a linearrecording velocity equal to or higher than 10 m/sec by setting the ratioPb1/Pw of the first bottom power Pb1 to the recording power Pw to 0.2 to0.5.
 7. The method for recording data in an optical recording medium inaccordance with claim 5, wherein the at least two recording marks areformed by setting a ratio of the shortest blank region interval to alinear recording velocity equal to or smaller than 20 nsec.
 8. Themethod for recording data in an optical recording medium in accordancewith claim 6, wherein the ratio Pb1/Pw of the first bottom power Pb1 tothe recording power Pw is set to 0.3 to 0.45.
 9. A method for recordingdata in an optical recording medium in accordance with claims 1, whereinthe pulse whose level is set to a level corresponding to the recordinglevel is constituted by divided pulses of a number corresponding to alength of the recording mark.
 10. The method for recording data in anoptical recording medium in accordance with claim 9, wherein the powerof the laser beam is modulated in accordance with a pulse train patternincluding a pulse whose level to set to a level corresponding to asecond bottom power lower than the first bottom power after the pulsewhose level is set to a level corresponding to the recording level. 11.The method for recording data in an optical recording medium inaccordance with claim, wherein the first bottom power and the recordingpower are set so that AH is larger than AL, where AL is a ratio of thefirst bottom power to the recording power when data are to be recordedat a first linear recording velocity and AH is a ratio of the firstbottom power to the recording power when data are to be recorded at asecond linear recording velocity higher than the first linear recordingvelocity.
 12. The method for recording data in an optical recordingmedium in accordance with claim 11, wherein the first linear recordingvelocity is set equal to or higher than 5 m/sec and the second linearrecording velocity is set equal to or higher than 10 m/sec.
 13. Themethod for recording data in an optical recording medium in accordancewith claim 11, wherein the first bottom power and the recording powerare set so that AH is larger than 1.5*AL and smaller than 5.0* AL. 14.The method for recording data in an optical recording medium inaccordance with claim 13, wherein the first bottom power and therecording power are set so that AH is larger than 2.5*AL and smallerthan 4.0*AL.
 15. The method for recording data in an optical recordingmedium in accordance with claim, wherein data are recorded in theoptical recording medium by projecting a laser beam having a wavelengthequal to or shorter than 450 nm thereonto.
 16. The method for recordingdata in an optical recording medium in accordance with claim 1, whereindata are recorded in the optical recording medium by employing anobjective lens and a laser beam whose numerical aperture NA andwavelength λ satisfy λ/NA≦640 nm, and projecting the laser beam onto theoptical recording medium via the objective lens.
 17. An apparatus forrecording data in an optical recording medium, which comprises a laserbeam projecting means for projecting a laser beam whose power ismodulated by a pulse train pattern including at least a pulse whoselevel is set to a level corresponding to a recording power and a pulsewhose level is set to a level corresponding to a first bottom power ontoa write-once type recording medium comprising a substrate and at leastone recording layer formed on the substrate, the laser beam projectingmeans being constituted so as to modulate the power of the laser beam inaccordance with the pulse train pattern in which a ratio Pb1/Pw of thefirst bottom power Pb1 to the recording power Pw is set to 0.1 to 0.5.18. The apparatus for recording data in an optical recording medium inaccordance with claim 17, wherein data are recorded at a linearrecording velocity equal to or higher than 5 m/sec.
 19. The apparatusfor recording data in an optical recording medium in accordance with 17,wherein a ratio of the shortest blank region interval to a linearrecording velocity is set equal to or smaller than 40 nsec.
 20. Theapparatus for recording data in an optical recording medium inaccordance with claim 17, wherein a ratio of the shortest blank regioninterval to a linear recording velocity is set equal to or smaller than40 nsec and at least two recording marks are formed.
 21. The apparatusfor recording data in an optical recording medium in accordance withclaim, wherein data are recorded at a linear recording velocity equal toor higher than 10 m/sec by setting the ratio Pb1/Pw of the first bottompower Pb1 to the recording power Pw to 0.2 to 0.5.
 22. The apparatus forrecording data in an optical recording medium in accordance with claim20, wherein the ratio of the shortest blank region interval to a linearrecording velocity is set equal to or smaller than 20 nsec and at leasttwo recording marks are formed.
 23. The apparatus for recording data inan optical recording medium in accordance with claim 21, wherein theratio Pb1/Pw of the first bottom power Pb1 to the recording power Pw isset to 0.3 to 0.45.
 24. The apparatus for recording data in an opticalrecording medium in accordance with claim 17, wherein the pulse whoselevel is set to a level corresponding to the recording level isconstituted by divided pulses of a number corresponding to a length ofthe recording mark.
 25. The apparatus for recording data in an opticalrecording medium in accordance with claim 24, wherein the power of thelaser beam is modulated in accordance with a pulse train patternincluding a pulse whose level to set to a level corresponding to asecond bottom power lower than the first bottom power after the pulsewhose level is set to a level corresponding to the recording level. 26.The apparatus for recording data in an optical recording medium inaccordance with claim 17, wherein the first bottom power and therecording power are set so that AH is larger than AL where AL is a ratioof the first bottom power to the recording power when data are to berecorded at a first linear recording velocity and AH is a ratio of thefirst bottom power to the recording power when data are to be recordedat a second linear recording velocity higher than the first linearrecording velocity.
 27. The apparatus for recording data in an opticalrecording medium in accordance with claim 26, wherein the first linearrecording velocity is set equal to or higher than 5 m/sec and the secondlinear recording velocity is set equal to or higher than 10 m/sec. 28.The apparatus for recording data in an optical recording medium inaccordance with claim 26, wherein the first bottom power and therecording power are set so that AH is larger than 1.5*AL and smallerthan 5.0*AL.
 29. The apparatus for recording data in an opticalrecording medium in accordance with claim 28, wherein the first bottompower and the recording power are set so that AH is larger than 2.5*ALand smaller than 4.0*AL.
 30. A write-once type optical recording mediumcomprising a substrate and at least one recording layer formed on thesubstrate and constituted so that data are recorded therein byprojecting a laser beam whose power is modulated by a pulse trainpattern including at least a pulse whose level is set to a levelcorresponding to a recording power and a pulse whose level is set to alevel corresponding to a first bottom power thereonto and forming atleast two recording marks in the at least one recording layer, theoptical recording medium being recorded with data for setting recordingconditions required for modulating the power of the laser beam inaccordance with the pulse train pattern in which a ratio Pb1/Pw of thefirst bottom power Pb1 to the recording power Pw is set to 0.1 to 0.5.31. The write-once type optical recording medium in accordance withclaim 30, which further comprises a light transmission layer, and afirst recording layer and a second recording layer formed between thesubstrate and the light transmission layer, and is constituted so thatthe at least two recording marks are formed by projecting the laser beamthereonto, thereby mixing an element contained in the first recordinglayer as a primary component and an element contained in the secondrecording layer as a primary component.
 32. The write-once type opticalrecording medium in accordance with claim 31, wherein the secondrecording layer is formed so as to be in contact with the firstrecording layer.
 33. The write-once type optical recording medium inaccordance with claim 31, wherein the light transmission layer is formedso as to have a thickness of 10 nm to 300 nm.
 34. A method for recordingdata in an optical recording medium comprising: projecting a laser beamonto the recording medium whose power is modulated by a pulse trainpattern including at least a pulse whose level is set to a levelcorresponding to a recording power and a pulse whose level is set to alevel corresponding to a first bottom power; forming at least tworecording marks in the at least one recording layer, setting a ratioPb1/Pw of a first bottom power Pb1 to a recording power Pw to 0.1 to0.5.
 35. The method for recording data in an optical recording medium inaccordance with claim 34 further comprising: recording data at a linearrecording velocity equal to or higher than 5 m/sec.
 36. The method forrecording data in an optical recording medium in accordance with claim34, in which the recording medium further comprises a light transmissionlayer, and a first recording layer and a second recording layer formedbetween the substrate and the light transmission layer, the methodcomprising: forming the at least two recording marks by projecting thelaser beam onto the optical recoding medium, thereby mixing an elementcontained in the first recording layer as a primary component and anelement contained in the second recording layer as a primary component.37. The method for recording data in an optical recording medium inaccordance with claim 36 wherein the second recording layer is formed soas to be in contact with the first recording layer.
 38. The method forrecording data in an optical recording medium in accordance with claim34 comprising: setting a ratio of the shortest blank region interval toa linear recording velocity to equal to or smaller than a selected valuewhen forming the at least two recording marks.
 39. The method accordingto claim 38 where in the selected value is 40 nsec.
 40. The method forrecording data in an optical recording medium in accordance with claim34 further comprising: setting the ratio Pb1/Pw of the first bottompower Pb1 to the recording power Pw to 0.2 to 0.51 to record the data ata linear recording velocity equal to or higher than 10 m/sec.